What a lovely boa! I love the busy, ornate pattern and the bit of chaining on the medallions near the tail. I'd definitely recommend quarantining them in a room separate from the rest of your collection if you can -- with boas of unclear origin, the threat of IBD is there.

Your boa's certainly an imperator, and the pattern definitely strikes me as Central American. Can't really narrow it down more from there, though. Good luck, and keep us updated!